The present invention relates to an apparatus for preventing over-discharge in various kinds of accumulator elements such as a secondary battery, primary battery and large-scale capacitors, etc. and, more particularly, to the over-discharge prevention apparatus which can improve utilization efficiency for the storage elements and to prevent erroneous (wrong) operation, that is, malfunction, at the time the electric power from the accumulator elements is cut to the electric and electronic apparatuses and instruments.
Conventionally, a battery package mounts therein secondary batteries as a power source for a portable electronic instrument and an auxiliary power system for electronic instruments and apparatus. The battery package is provided with an over-discharge prevention mechanism as well as an over-charge prevention mechanism so that troubles such as degradation of battery properties and/or leakage of a battery liquid at the time of over-consumption of the installed batteries can be prevented.
FIG. 5 shows a block diagram of a typical structure of the conventional over-discharge prevention mechanism, which is generally composed of a voltage detector 2 for monitoring an electric voltage of the battery and a switching portion 1 connected in series with batteries B1 and B2 (in an example of two cells connected in series) between terminals T1 and T2. When the battery voltage falls below a discharge extinction voltage, the voltage detector 2 is driven to switch OFF the switching portion 1 to thereby stop the electric supply to electronic apparatuses and instruments.
However, with respect to electronic apparatuses and instruments such as personal computers and digital portable telephone instruments which require data processing, the data in the process or are destroyed when the power supply is stopped due to the over-discharge detection.
Therefore, these electric apparatuses and instruments have been provided with a power source detection mechanism so that the remaining battery remanent voltage is assumed from a voltage value VT of the power source in the battery package to judge in advance the state of battery consumption, and then an operation of the electronic apparatuses and instruments are accurately stopped before the battery output is cut off so that the data and information are reliably saved and protected.
However, since the judgment of the battery consumption is generally provided with some marginal regions in order to reliably stop the operation of the electronic apparatuses and instruments so that the electronic apparatuses and instruments are stopped even when the remaining capacity of the battery is fully within the usable region, it has been difficult to take out the battery capacity of the battery package to a maximum extent.
In addition, in the battery package of the illustrated example of FIG. 5 in which a plurality of battery cells Bl, B2, ( . . . Bn) are connected in series, the balance of cell voltages V1, V2, ( . . . Vn) is detected by the voltage detectors M1, M2, ( . . . Mn), respectively, and a logical sum (logical OR) of the detected outputs drives the over-discharge prevention mechanism to cut off the power supply and. Accordingly, it has been quite difficult to externally judge accurately the consumption of the battery. Therefore, a voltage margin of the voltage detection in the electronic apparatuses and instruments is inevitably further increased, with the result that an efficiency of the consumption or usage is further degradated.